Follow up observations

The follow up 21cm synthesis observations on the galaxies found by this survey are essential for a number of reasons. First, Arecibo is capable of detecting galaxies as far as 6 arcmin from the center of the beam. The positional accuracy is too poor to make unambiguous identifications with cataloged galaxies or galaxies on the DSS. Second, reliable flux measurements are necessary in order to construct an HIMF. Flux measurements from the survey data can be poor if the detected galaxy is more extended than the survey beam or if it is detected at a large distance from the center of the beam. Finally, we have found that some signals were actually caused by pairs or a small group of galaxies. This was not always obvious from looking just at survey spectra.

We took short (20 min) 21cm line observations of 55 of the 61 detected galaxies with the VLA during the D-Configuration session in May 1995. The remaining six galaxies were too close to the sun at the time of the observations. These short observations were of sufficient sensitivity to construct HI maps and global profiles of 52 of the 55 potential galaxies. The signal of three systems fell below the detection limit.

Optical follow up observations were carried out on the 2.5m Isaac Newton Telescope on La Palma. We have been able to make B-band images of 24 galaxies during two observing runs in October 1995 and February 1996. Additional time has been awarded to observe the remaining galaxies. So far, we have been able to make optical identifications of all HI selected galaxies. No isolated HI clouds without stars have been found.

б© Copyright Astronomical Society of Australia 1997